The upgrade is incomparably more potent then volks stg, why should it cost the same or less?
Especially now that volks and PFs cost almost exactly the same.

???
Because the fussiler early game is so incredibly fucking weak that its retarded, they don't beat anything early game aside from ~~maybe~~ engineers but even those get close once flamers come out.
Not only that but if you go t2 you actually sacrifice getting the medkits for the army, or even worse, forces you into not using nades at all for the early game.

So basically it.
A pigeonholes you into the shitty t1 unless you want to make some major sacrifices for ultimately a very minor gain.
B Isnt that much more potent
C Is doctrinal.

Imo fussi upgrade should be 60-70 muni, your already paying resources for a shitty squad that only becomes viable once they have said upgrade, whatever cost you pay less in muni is more or less exchanged for worse early game.

Svts has dps on par with stg volks at all ranges (and better at super close iirc) which means you pretty much win at all ranges regardless of what you do once you reach vet 3 lol. that added with being 6 men with 4 svts vs 3 ppsh, the only advantage of ppsh is hit the dirt but even that is like, meh.